Micro:
As I said, you will have to "change the Law" in order to pitch down, otherwise, in Normal Law, the Overspeed Protection will take control.

To those who say that, this is a very unlikely situation, I would like to ask if you think this would be absolutely impossible to happen?

Altitude variations affect IAS via the static ports. "Turbulent air" as such does not.
Mach buffet is a violent high frequency shake of the aircraft that is very different from turbulence-induced g-variations. The airplane had left the turbulence before it stalled.
Once stalled, the airplane is effectively uncontrollable in roll, its reponse to a roll input is often opposite to that commanded, at any rate quite different from normal.

No. In Alternate 2 law, roll is direct. Meaning sidestick deflection gives proportionnal control surfaces deflection. This is different than the normal mode, and FBW doesn't try anything here, no "masking".

What flight are you talking about :confused:
If still AF447 : sorry, this one never get to overspeed.

Same question. If that's AF447, I fail to see anything suggesting any of the crew members ever understood the stall situation.

Two remarks:
- It still remain to be proved that elevators only aren't enough to maintain stall (at a lower AoA than that obtained with the help of the THS, maybe). IIRC knowledgeable peope (of which I'm not) suggested otherwise.
- What do you mean by "the lack of autotrim on Boeings"?

[edit] May I suggest we move to the AF447 thread if I undestood correctly that was the topic at hand? We're hijacking flyburg's thread, here.

This may not be apparent as the output of the altitude calculation from the statis prerssure to the altimeter is filtered, but I assure you that it does.I am talking about the stall buffet. The aircraft was at that point flying too slowly to induce a mach buffetThere is most definitely a degree of residual positive roll control in an aircraft of conventional design when deep stalled. How much exactly for a particular aircraft in a particular circumstance is a question nobody can answer for sure as this has to my knowledge never been tried in a large aircraft (and lived through), but the windtunnel data, flight test data and computer models which are used in the aerodynamic models in simulators leave little room for doubt. I will concede however, that this is way beyond what any sim is certified for for flight training.

Fair enough, it seems I had my modes mixed up.Have you read the CVR transcipt?My point was that with elevators alone the aircraft will drop the nose again when the elevator backpressure is released, but this may no longer be the case when the THS is trimmed fully aft.I know of no Boeing type which has an Airbus type autotrim system that automatically trims the THS to relieve pitch input. In manual flight, even the 777 and 787 have to be trimmed manually for airspeed using the trim switches. This does not take into account some functions where the trim is adjusted automatically with flap and speedbrake deployment, but the fact remains that the pilot is almost completely out of the loop with regards to the THS in the Airbus.

I am talking about the Mach buffet that AF447 was entering at 02:10:55 at M.67 that is shown on page 43 of Interim Report #3 and described in the associated text.

[edited] A-FLOOR, I moved my answer to the AF447 thread, here, in order to comply with my own remark re: "hijacking" of the present thread ;)

Hmm, I'm afraid I'm not sure to which case you are referring?
In case of the A340 Zoom Climb it was overspeed protection that send the aircraft into a climb but it did not stall. AoA protection law kicked in and kept it at Alpha_Prot. No stall here, and no alternate law either.

If you are referring to AF447, there was no overspeed event, it was in alternate law 2 due to the ADIRU's signalling Unareliable airspeed (Icing of pitots) and it was sustained NU commands by the manually flying PF that caused the THS to finally support his efforts and go to a significant NU Trim setting. This combined with further mainly NU commands on the sidestick kept it in the stall.

Alpha_Max is a HARD protection which cannot be overriden as long as it's active (not the case in AF447 due to Alt2). High speed protection might win against Alpha_Prot but not against Alpha_Max
It is not THAT easy to fool the Airbus protections. That takes much more finesse and or bad luck (stuck AoA vanes in Perpignan).

@flyburg: Apologies for also taking part in the AF447 thread hijacking ;-)

Two A340 'level bust' incidents have been discussed recently on this forum: TC-JDN on 2/10/2000 and F-GLZU on 22/07/2011. In both cases there was an overspeed warning but the overspeed protection was not activated.

I was referring to the second one where at least the FDR trace shows 2 overspeed events right at the beginning of the incident.
See http://www.bea.aero/docspa/2011/f-zu...f-zu110722.pdf
page 18.
But indeed it seems the pitch up was due to Sidestick input although the AoA starts to increase prior to deflection of the S/S which I attributed to overspeed protection. Looking closer at the traces the pitch only starts to increase after the NU S/S commands.
In the text overspeed protection is also not explicitely mentioned, therefore I come to agree to your statement and stand corrected.

Ahem, sorry but...
"Au cours de l’événement, la protection haute vitesse ne s’est pas activée."
=> "Throughout the event, the high speed protection did not activate."
Footnote 4, page 3.

Yes, static ports can get iced over in flight.

That may be true.

However, the static is very sensitive to airflow variations. Put a minor obstruction on the skin somewhat upstream and the PEC can alter substantially from what the AFM suggests.

Keep in mind that a lot of effort in the certification test program goes into establishing the PEC information for the AFM.

Use of THS
 

Good thoughts re use of THS as recourse of last resort. One perhaps could file this away under "what to do when all of the usual drills and memory items aren't working" file. I suspect however that the crew of AF447 never really knew that they were in a stall, nor what their real AoA was in the last minutes of flight......:sad:

B777 has no autoreim in that sense, but it is not a conventional THS either. It moves without pilot inputs, same as elevators, depending on actual speed and trim reference speed, which is what you select with the switches.

So, if speed is wrong, if speed is overspeed (for the computers, I mean) what would happen in a B777. Its protections are different tha those of airbus. No uncommanded pitch up or down, but there are forces induced in the control column to cue the pilot. In this case it would mis,ead the pilot, right? It would be too stiff for pushing, I deem...

Computers are computers. They have a big problem. What happens when they are doing the wrong thing without detecting it is tthe wrong thing.

Just a small point of order here. Boeing offers the AOA in all of it's current airplanes. Delta and American are the only airlines that I know for sure have the AOA in the 737NG and 777 series aircraft.:ok:

"Computers are computers" - garbage in/garbage out.

However, the fact remains that accident rates continue to fall, not only per million flights, but in absolute terms. Yes, we need to continue to develop the software models, but the argument that flying is more dangerous because of increased computerisation is simply false. I am not convinced it's even possible to argue that aircraft with computerised protections are more dangerous than those without.

Absolutely.

I'm talking about the different nature of computers as opposed to mechanical systems.

When computers are involved, wrong data that can't be dismissed by the computers as wrong, can make the computer make very nasty things. The more complex the system is, the more involved one computer in the system and the more systems interface that computer, the worse effects such a malfunction will have.

Wether it is a Boeing or an Airbus, computers are computers.

Computers are protected against that in various manners, like "watchdogs", "voting", control and monitoring dual channels and "dissimilar redundancy". When a computer is not working properly, it is very important that the computer is declared invalid, either by itself or by other computers, so that its outputs are neglected.

The simultaneous and identical freezing of all three pitot tubes will make all three computers be in error, which makes impossible to detect by voting. So it is necessary some added function to avoid that situation, such as probe ice detectors or a "reasonableness check of IAS" using data other than pitot, I think there is already something like that invented.

I'm still curious about what would happen in a B777

Oooopsie, now that you point me to it....

Guess I need to give my glasses a good cleaning :}


On a more serious note:
Is there any documented case of an overspeed protection induced Pitch Up in an A330/340? Apart from this one where I wrongly assumed it was the overspped protection that initiated the climb I'm not aware of any other suspected case on these types. Did I oversee something?
Has it really never been used in anger?

MEIKLEOUR #59
AVEROW #72

If " The THS is NEVER NORMALLY moved by the Crew in flight... " it might tend to be forgotten.

If a car with hydraulic brakes has a hydraulic leak, the hand brake is a separate system which can be used... And it should be used, just occasionally, to remind the driver that it is still there.

( A family car had a hydraulic leak recently. Luckily the young driver DID remember. All was well...)